Perched on a hill overlooking Swansea Bay, Oystermouth Castle has guarded the Gower Peninsula for more than nine centuries. The Grade I listed fortress, known in Welsh as Castell Ystum Llwynarth, conceals one of medieval Wales' most remarkable secrets: a 14th-century chapel hidden within its walls, adorned with 700-year-old paintings that remained unseen by the public for centuries.
Norman Foundations and Welsh Resistance
The castle's origins trace back to 1106, when William de Londres of Ogmore Castle established the first Norman stronghold on the site following the Norman capture of Gower. The original structure was a ringwork and bailey fortification built atop an earlier Welsh fortification called Caer Tawy, which had guarded the River Tawe. No trace of this earliest phase remains today.
The castle's early history was turbulent. In 1116, Welsh forces from Deheubarth retook the Gower Peninsula and burned the castle, forcing William de Londres to flee. The fortress was likely destroyed again in 1137 when the Princes of Deheubarth reclaimed the territory. In 1215, Llywelyn the Great captured Gower, and by the time the Welsh were expelled in 1220, the Londres family had died out.
Henry III returned the barony of Gower to John de Braose, who rebuilt both Swansea Castle and Oystermouth Castle in stone. Throughout the 13th century, the de Braose family constructed the high curtain wall, internal buildings, chapel, basements, and three-storey residential buildings with fireplaces and garderobes that visitors see today.
The Rise of a Principal Residence
By the late 13th century, Oystermouth had supplanted Swansea Castle as the principal residence of the Lords of Gower. The castle received royal attention in December 1284, when Edward I paid a brief visit during his campaigns in Wales. However, by 1331, the Lords of Gower had relocated elsewhere, and the castle began its long decline in importance.
A survey from 1650 described Oystermouth Castle as "an old decayed castle" of "no use, but of a very pleasant situation." The structure was restored during the 1840s by George Grant Francis while under the ownership of the Duke of Beaufort. In 1927, the Duke transferred ownership to Swansea Corporation, ensuring the castle became a public heritage asset.
Alina's Chapel: A Medieval Masterpiece Revealed
The architectural highlight of Oystermouth Castle is its chapel block, added during the 14th century. The chapel is traditionally attributed to Lady Alenora de Mowbray, wife of Lord John Mowbray, though some sources credit Aline de Breos (also known as Alina de Breos), daughter of William de Breos III, Lord of Gower.
Situated on the second floor of the chapel block, the space features 14th-century traceried windows. The east window retains what experts describe as the finest tracery of its period in south-east Wales. During conservation work, workers discovered remnants of ornate medieval paintings dating back to the 14th century. Cadw analysis revealed a double-arched canopy containing figures of angels, with clear elements including a wing with multiple feathers and circular shapes forming a head with yellow hair surrounded by a nimbus.
A Bridge to the Past
For centuries, Alina's Chapel remained inaccessible to the public. That changed in 2011, when a Β£1 million refurbishment project culminated in the installation of a 30-foot glass viewing bridge. The structure, which opened to visitors in July 2011, provides access to the chapel for the first time in hundreds of years.
The restoration was funded through a partnership between the Welsh Government and Cadw (Β£400,000), the European Regional Development Fund (Β£585,000), the Heritage Lottery Fund, and Swansea City and County Council. Works included a new visitor centre, educational space, improved accessibility, and a refurbished toilet block.
Exploring the Castle Today
Visitors to Oystermouth Castle can explore the 12th-century keep, the earliest stone building on the site. Originally a free-standing rectangular structure entered through an arched doorway, the keep represents the Norman foundation of the fortress. The high curtain wall features a wall-walk offering panoramic views across Swansea Bay, Mumbles, and the Gower Peninsula.
The gatehouse walls curve inward, showing where two round towers were intended to be constructed, though it remains unknown whether they were ever completed. A dimly lit narrow passage, illuminated by narrow slits, leads to a spiral staircase glimpsed through the openings.
The three-storey residential ranges feature fireplaces and garderobes on each floor, with barrel-vaulted basements below. These buildings demonstrate the sophisticated lifestyle of the medieval nobility who once called Oystermouth home.
A Swansea Landmark
Today, Oystermouth Castle stands as one of Swansea's principal heritage attractions. The castle community co-ordinator manages a programme of events throughout the year, while the multi-functional room developed below Alina's Chapel provides space for educational activities and gatherings.
For Swansea residents and visitors alike, the castle offers a tangible connection to the Norman conquest, Welsh resistance, and medieval aristocratic life that shaped this corner of Wales. The glass bridge to Alina's Chapel ensures that one of the region's finest medieval secrets is no longer hidden from view.
